The invention concerns a device and a method of transferring bulk material from a reservoir or a holding space through a lock space into a pneumatic conveyor line, wherein the lock space is closable in relation to the reservoir or holding space by a movable closure body and at least one counterpart sealing element in opposite relationship thereto in its path of movement.
Devices of that kind are to be found in EP 0 166 959 B1; at its intake side it has a conical closure body, in the center of which a vent opening surrounded by a resilient collar is cyclically closed and opened by a stepped cone of elastic material. The seal which is disposed in opposite relationship to the closure body is to be deformed by the conveyor air which is supplied theretoxe2x80x94through an annular passage disposed therebeneathxe2x80x94in such a way that the conveyor air issues uniformly directed on to the closure body and thus in the closure movement blows the closure bodyxe2x80x94seal contact line free of product. That is intended to ensure a pressure-tight sealing action for the inner lock space towards the supply reservoir. Release of the compressed air at the end of the conveyor cycle is effected directly by the now open central opening in the closure cone into the supply reservoir which is disposed thereabove and which is filled with the product to be transported. The air has to flow through the pores of the product.
It has been found that the distribution of air through the deformable seal is not so uniform that the closure body always closes against the sealing edge of the seal in pressure-tight relationship. In addition with strain gauge measurements made on the walls of the reservoir it was established that the discharge air which flows through the pores in the product, when the reservoirs are of considerable heightxe2x80x94for example in silosxe2x80x94builds up pressures which make it necessary for those containers to be of a relatively great wall thickness, which thus involves higher cost levels.
That deficiency was overcome by the invention described in EP 0 270 012 B1, insofar as the air released from the lock space is passed through a tube portion at the closure cone with an opening arranged above the flow path of the bulk material, into an intake housing, and is discharged through a central opening in the intake housing. When the pressure in the lock space has fallen, the closure cone moves downwardly and the opening in the tube portion is closed in that position of the closure cone by a resilient cone tip. The opening is only open in the air release procedure; both in the conveyor mode of the apparatus and also when the bulk material is passing into the lock space, the opening is closed by the resilient cone tip. Therefore the air which is displaced by the bulk material as it flows into the lock space must be passed in counter-flow relationship through the inwardly flowing bulk material. That increases the length of the period of time required to fill the lock space.
A not inconsiderable duration for the filling operation is also involved in the arrangement of EP 0 166 951 B1. In that case, provided beneath the closure element for the outlet of the lock space is a feed line for conveyor air. The major part of the conveyor air enters here, at relatively high flow speed, due to the small cross-section involved. There is a pressure drop in the discharge housing, due to the flow being accelerated in the cross-section of the mouth opening. In a condition of co-operation with the product-air mixture which subsequently flows out of the lock space and which is discharged through the conveyor conduit, that produces an upward and downward movement of the discharge flap. As a result, the switch actuated by the discharge flap initiates vent operations before the lock container is completely emptied. Wear occurs in the discharge air lines and there is a loss in conveyor capacity due to the fact that the bulk material does not entirely discharge from the lock space. If the air feed is arranged about 3 meters downstream on the conveyor line, the described effect is eliminated, as can be seen from EP 0 270 012 B1. As in that case however the transport of product from the discharge housing to that air feed-in location only has to be overcome by the amount of air added at the closure head at the intake end, the conveyor capacity is reduced.
The conveyor capacity to be achieved depends on the duration of the cycle time. The cycle time is primarily composed of the emptying time and the filling time of the lock space. The emptying time is substantially dependent on the properties of the bulk material, the conveyor path, the conveyor cross-section, the conveyor air speed and the conveyor pressure. The filling time of the lock space is in turn substantially determined by the properties of the bulk material, the feed flow cross-section, the open cross-section of the closure head and the flow conditions in the opened closure head when the bulk material is flowing into the lock space. It has been found that the introduction of bulk material takes place reliably and quickly only with relatively grainy and heavy bulk materials, for example quartz sand and sugar in crystal form. In the case of light bulk materials in dust form the introduction thereof is uncertain and the introduction time is very long so that these devices do not achieve adequate conveyor capacities.
The device disclosed in EP 0 270 012 B1 also provides that light materials to be conveyed are fluidised in the intake housing by the air which rises in counter-flow relationship, and substantially fill the intake housing. Upon next venting of the lock space considerable amounts of the material to be conveyed are then discharged through the central opening of the intake housing. In practice those amounts of conveyor air in those apparatuses can be fixedly set by means of adjustable throttle valves; there is no regulation of the pressure and loading conditions of the conveyor flow. As a result it is not possible to make optimum use of the energy of the conveyor air which is introduced into the system. Sealing elements of elastic material are required in the known devices for permanently pressure-tightly closing off the lock space. The admissible temperature range is greatly restricted by the properties of those materials.
With knowledge of that state of the art the inventor set himself the aim of providing a simple device and a conveyor method for same, with which the levels of conveyor capacity can be increased and even light bulk materials in dust form can be transferred into a conveyor line. The invention further seeks to provide that the conveyor operation is more economical and even hot materials being conveyed can also be fed into a conveyor line.
The teaching of the independent claim provides for attainment of that object; the appendant claims set forth advantageous developments. The scope of the invention also embraces all combinations of at least two of the features disclosed in the description, the drawing and/or the claims.
In accordance with the invention the closure body has at least one vent opening which opens into an air discharge passage and is closable upon the upward closing movement of a stroke element with a sealing body; the downward opening movement thereof is also shorter than the downward movement of the stroke element with the sealing body. In that respect it has proven to be desirable for the closure body to be so designed that it enlarges from a narrow cross-section forming an inner sealing edge in a funnel-like configuration towards the sealing body and the narrow cross-section is an annular seat for the sealing body in the closure position.
In accordance with further features of the invention an air discharge passage is taken from the vent opening of the closure body to an aperture in an intake housing which is arranged upstream of the lock space, and the air discharge passage is connected to an air discharge line at the aperture in the operative condition. In addition the sealing body should be provided with a conical tip for the annular seat.
The closure body which is provided at the intake end in the lock space and which seals against a peripherally extending edge in the closure position therefore has at least one vent opening which opens into an air discharge passage and is closed in the upward closing movement with the sealing body.
By virtue of that arrangement the air which is displaced out of the lock space by the inflowing bulk material can leave the lock space through the vent opening of the closure body without retarding the inflowing bulk material. If in addition air is sucked away at the intake housing when the bulk material passes into the lock space, the discharge of air from the lock space is accelerated and thus the bulk material intake time is further reduced. Particularly for light bulk materials of fine grain size, it is advantageous for the vent opening in the closure body and the air outlet opening of the intake housing to be connected independently of travel. In accordance with the invention that can be effected for example by means of a concertina member or by hollow profile members which are guided telescopically one within the other. By virtue of those features discharge of the air takes place in the optimum fashion and the required bulk material intake time is very short. Those passages can easily be so designed thatxe2x80x94as statedxe2x80x94the possible opening travel of the closure body is less than the opening travel of the stroke drive.
Fans but in particular injectors which can very advantageously be arranged in an air discharge passage are suitable for discharging the air. A suitable form of stroke drive is in particularxe2x80x94per se knownxe2x80x94pneumatically actuated bellows-type cylinders and double-acting pneumatic cylinders whose upward and downward movement is produced by air acting alternately on the two piston surfaces, but also single-acting pneumatic cylinders with a plunger piston. In the arrangement with a plunger piston the closing movement is effected by means of compressed air, while the opening movement is produced either by the weight of the plunger piston and the closure body or by virtue of a reduced pressure being applied to the piston surface. The opened position is then achieved by a suction effect on the plunger piston.
It is possible to combine with that device arrangementsxe2x80x94for example pins and guidesxe2x80x94which rotate the closure body somewhat about its axis in its upward/downward movement. In that way the contact surfaces of the closure body and the peripherally extending sealing edge are permanently smoothed, kept groove-free and permanently remain sufficiently capable of affording sealing integrity, even if the closure body and the peripherally extending sealing edge comprise tough material, for example steel. That affords a design configuration of the device according to the invention even for hot bulk materials. If the seal which forms the peripherally extending sealing edge comprises elastic material, it can be so designed that the closing movement of the closure body is at least in part converted into a reinforcement of the sealing action. By virtue of that design configuration it is possible to produce markedly simpler devicesxe2x80x94in particular for introducing substances in granule form into pneumatic conveyor linesxe2x80x94than is possible with the devices in accordance with the state of the art.
As is known, the feed of conveyor air can be effected on the one hand into the lock space through an air curtain which is directed on to the closure body and on the other hand, as viewed in the flow direction, downstream of the discharge cross-section of the lock space. If a valve is also present at the lock space outlet cross-section, then in accordance with the invention an air curtain can also be directed here on to the sealing edges of the valve for the purposes of cleaning those sealing edges. That is particularly advantageous when that valve is of a tough nature.
In accordance with the invention the feed of the conveyor air downstream of the valve should be implemented over a large area. In that way fluctuations in pressure emanating from the fed-in conveyor air in that region are avoided. In accordance with the state of the art, the two air flows can be set by means of throttle valves or aperture devices. It is however more advantageous, in accordance with the invention, to control the two air flows in accordance with the fluctuating pressure in the lock space or at the beginning of the conveyor line; in that way it is possible to make optimum use of the energy of the supplied compressed air.
Until a preselected conveyor pressure is reached, compressed air is primarily fed to the lock space, then to the air feed-in location which is downstream of the lock space, until the conveyor pressure has fallen below the preselected conveyor pressure. That provides that the ratio of the amount of material being conveyed to the amount of conveyor air is always kept almost at the optimum, while for a proportionate air flow the air feed-in locations can be connected by passages.
Particularly when dealing with materials to be conveyed which have a poor capacity for resistance to air, it is advantageous to couple an air in-feed at the beginning of the conveyor pipe, to the air in-feed at the valve which is connected downstream of the lock space. It is also possible to use a plurality of air feed-in locations along the conveyor line, which are controlled from the device according to the invention. Switching of the air in-feed can be effected pneumatically or electropneumatically.
It is also in accordance with the invention, in a device as set forth in the opening part of this specification for introducing bulk material from a reservoir or a holding space through a lock space into a pneumatic conveyor linexe2x80x94in which the lock space is closable in relation to the reservoir or holding space by an axially movable closure body and at least one counterpart sealing element disposed in opposite relationship thereto in its path of movementxe2x80x94for one of the counterpart sealing elements to be in the form of a flexible sealing surface which is clamped in cross-section at one end and for the other to be in the form of a sealing edge which entrains the free edge region of the sealing surface and increasingly deforms it in the path of movement; that sealing surface should preferably be a ring surrounding the closure body. Protection is claimed separately in respect thereof, and in respect of a design configuration in which the sealing surface is a sealing lip which is clamped in cross-section at one end on the housing side and the closure body is provided with at least one projecting sealing edge and with at least one entrainment portion which engages under the sealing lip. That thus affords an extremely efficient and simple sealing region.
The feature of inwardly deforming the lower edge region of the closure body which enlarges funnel-like in opposition to the stroke direction, forming the sealing edge and an inclined edge portion, makes it possible on the one hand easily to produce the required sealing edge and on the other hand to afford on the inclined edge portion the entrainment portions which then project therefrom.
In accordance with another feature of the invention the thickness of the sealing lip is greater than the spacing of the entrainment portion or portions from the sealing edge so that same can engage into the lip edge after the edge region has been lifted by the entrainment portions.
In another embodiment the deformable seal is part of the closure body and its lip edge is directed towards the edge of a stationary opening in the device.
At any event it has proven to be desirable for the sealing lip to be clamped at one end between two flanges. In addition the sealing lip is to be inclined downwardly in cross-section at an angle from its clamping location so that its lip edge faces in opposite relationship to the stroke direction. The latter moreover in the relieved position of the sealing lip is to extend substantially parallel to the stroke travel or the longitudinal axis of the device.
The method according to the invention is distinguished in that air displaced from the lock space during the inward transfer of the bulk material is discharged through at least one vent opening in the closure body, which goes into an air discharge passage. The displaced air can also be sucked out of the lock space. It has proven to be advantageous for the conveyor air to be fed to the described device at at least two feed-in locations and for those feed-in locations to be controlled alternately in dependence on a predetermined reference value of the conveyor pressure and an instantaneous actual value of the conveyor pressure.